The disclosure relates to a variable displacement hydrostatic axial piston motor of bent-axis construction, which comprises a drive shaft, a cylinder drum that can be pivoted in a pivoting plane, a one-piece port plate, which has a central plane extending parallel to the pivoting plane and on which there are two working ports with flat port surfaces, one of which is situated on one side of the central plane and the other is situated at the same distance from the central plane on the other side of the central plane. For adjustment of the displacement, the hydrostatic axial piston motor has an adjusting device, which comprises an adjusting piston arranged in a cylindrical receiving space of the port plate, a control valve arranged on a first side of the port plate and having a control valve piston, and a feedback spring, which is arranged in the port plate, is clamped between the adjusting piston and the control valve piston and is arranged together with the adjusting piston and the control valve piston on one axis. A counterbalance valve having a counterbalance spool is provided, which is intended to reduce the risk of overspeeding and cavitation of the axial piston motor in an open hydraulic circuit. To limit the pressure, there are furthermore two secondary pressure-limiting valves, which are inserted as cartridge-type inserts into the port plate, of which one secondary pressure-limiting valve is arranged on one side of the central plane and the other secondary pressure-limiting valve is arranged on the other side. The secondary pressure-limiting valves ensure that the pressure is not too high when the axial piston motor is operating as a pump, something that can occur under a negative load.
A hydrostatic axial piston motor having the above features is known from datasheet RE 91616, Edition 05.2016, for example. In this datasheet, pages 27 to 29 show various versions of a hydrostatic axial piston motor, the displacement of which can be varied with the aid of an adjusting device. The adjusting piston of the adjusting device is a differential piston, which is acted upon over an annular surface by the high pressure prevailing in a port of the axial piston motor and the larger piston surface of which delimits an adjusting chamber, which is connected to the control valve. The control valve piston of the control valve is acted upon in one direction by a force which corresponds to the level of a control signal and is, for example, the force of an electro-proportional magnet or a force produced by a control pressure and is acted upon in the opposite direction by the force of a feedback spring, which is clamped between the control valve piston and the adjusting piston, with the result that the force exerted on the control valve piston by the feedback spring depends on the position of the adjusting piston. Depending on the level of the force corresponding to the control signal, the adjusting piston is thus moved by the control valve to a position such that the spring force is equal to the force specified by the control signal.
In the case of the automatic high-pressure-dependent adjustment discussed in said datasheet too, the adjusting piston is a differential piston, which is acted upon over an annular surface by the high pressure prevailing in a port of the axial piston motor and the larger piston surface of which delimits an adjusting chamber, which is connected to a control valve. The control valve piston of the control valve is acted upon in one direction by a spring, which is set to a fixed value, the force of which, which is exerted on the control valve piston, is therefore not dependent on the position of the adjusting piston, and is acted upon in the opposite direction by the high pressure.
A hydrostatic axial piston motor of bent-axis construction with electro-proportional adjustment of the displacement is known from DE 196 53 165 C2. This axial piston motor has an adjusting device which comprises an adjusting piston, which is arranged in a cylindrical receptacle of the port plate and is designed as a differential piston, a control valve arranged on a first side of the port plate and having a control valve piston, and a feedback spring, which is arranged in the port plate and is clamped between the adjusting piston and the control valve piston. The axes of the adjusting piston, the feedback spring and the valve piston are aligned with one another and are therefore arranged together on one axis. The control valve piston is acted upon in one direction by the force of the feedback spring and in the opposite direction by the force of an electro-proportional magnet. In the event of a non-equilibrium of forces, the control valve piston is moved out of its central position, in which it shuts off a control valve port connected to an adjusting chamber with a small positive or negative overlap or a zero overlap, with the result that pressure medium is fed to the adjusting chamber at the adjusting piston or displaced from the adjusting chamber, causing the adjusting piston to move and, in the process, to change the force exerted by the feedback spring on the control valve piston until an equilibrium of forces is reestablished at the control valve piston and the control valve piston once again moves into its central position.
In the case of the versions of a hydrostatic axial piston motor which are shown on pages 27 and 28 of datasheet RE 91616, Edition 05.2016, a brake valve having a counterbalance valve and two check valve combinations, each consisting of two check valves, which are arranged in a separate brake valve housing, is attached to the port plate of the axial piston motor. The secondary pressure-limiting valves are arranged in the port plate perpendicularly to a central plane of the port plate.
Pages 32 and 33 of datasheet RE 91616, Edition 05.2016 show versions of a variable-displacement hydrostatic axial piston motor in which the adjusting piston of the adjusting device for the displacement is a synchronizing piston, i.e. a piston which has two effective areas of equal size. This can be inserted easily into a blind hole in the port plate, wherein two adjusting chambers are formed in front of the two ends of the adjusting piston after the closure of the blind hole. The manner in which the displacement is adjusted means that there does not appear to be any particular advantage in any position of the control valve in relation to the adjusting piston, and therefore there is very great freedom in the arrangement of the control valve. These versions of a hydrostatic axial piston motor have a port plate into which the counterbalance valve and the two check valve combinations are integrated.